I've recently ridden an 05 model Tuono, and can say its quite comfortable for my frame (6' and 220 lbs). The motor was impressive, and the newer ones have more hp >

I have not ridden an S4R or S4Rs. The dealer network is now getting better since Piaggio bought Aprilia. Go visit
www.apriliaforum.com and start getting a feel for the brand, dealers, etc. The forum is actually run by a dealer out of Texas that a lot of the folks get their parts from (similar to Duc of Seattle on this board).
I am also going to be getting either an S4Rs or Tuono in the coming months.......and am leaning toward the Tuono. Most folks feel the maint. costs would be less.........and for me, I don't have a dealer near me for either brand so that aspect is the same for me.
Have fun bike shopping.......I love the journey as well as the destination [thumbsup]